1. Field of the Invention
This invention relates to new and useful soy products and methods for producing the products.
2. Prior Art
The increasing evidence that a proper diet is linked to good health and the prevention of diseases has led consumers to demand products that help develop healthy diets with more nutrients and less fat, cholesterol, and calories. Food processors interested in satisfying consumer demand are looking at healthy ingredients to develop such food products. One source for healthy ingredients is the soybean. The increasing evidence that soybeans may help prevent and treat certain diseases, such as heart disease and cancer, has renewed consumer and processor interest in soybeans as a source for foods and ingredients. Food processors are familiar with many uses of soybeans because of their multifunctional value, natural ingredients, and reasonable prices.
Many processors prefer to use soybeans because of their high protein content and their ability to mimic animal products such as meat, eggs, or milk. Processors also prefer soybeans because of their broad consumer appeal. Food processors have been careful and reluctant to use soybeans as ingredients in their finished products because soybeans have several negative factors. First, soy meal has a very beany flavor. Second, most soybean meal has reduced protein solubility, normally less than 50% because most of the current processes use heat to deactivate the trypsin inhibitors and remove residual hexane from the extraction process. Third, because the protein solubility is reduced and the trypsin-inhibitors have not been completely deactivated, the body absorbs less protein. Finally, soy meal causes flatulence and bloating and has a chalky texture stachyose and raffinose are present.
In conventional processing of soybeans, soy protein flour, soy protein concentrate, and soy protein isolates are all produced in different non-integrated sections of the plant. Further processing of the soy meal is carried out to produce soy protein isolates and soy protein concentrates separately after soy oil extraction when the extraction solvents have been removed. Soy protein concentrates are produced by either an acidic extraction or an aqueous/alcohol extraction of soluble carbohydrates, whereby at least 10% of the protein is lost. On the other hand, soy protein isolates are normally produced in two steps. First, the soluble carbohydrates and proteins are separated by alkaline extraction and centrifugation. Second, the proteins are precipitated by acid and/or aqueous/alcohol wash and removed by centrifugation. Normally, 30-35% of the proteins is lost because the alkaline extraction causes a loss of insoluble proteins and the acidic/aqueous-alcohol extraction causes a loss of soluble proteins. Under these conditions, the soy protein is denatured and loses its solubility, resulting in a low protein dispersibility index (PDI) (also referred to as the protein digestibility index or the nitrogen solubility index (NSI)), which is defined as the amount of digestible (soluble) protein relative to the overall amount of protein within a material.
Soy meal contains naturally occurring proteins known as trypsin inhibitors that block the action of the trypsin enzyme within the human digestive tract. During protein digestion, the pancreas produces the trypsin enzyme that cleaves the amino acid bonds within proteins to make those proteins more digestible. Unfortunately, the trypsin does not cleave the amino acid bonds within the trypsin inhibitor proteins in soy meal. Rather, the trypsin inhibitor proteins within the soy meal bond with the trypsin enzymes, thereby preventing the trypsin enzymes from cleaving the amino acid bond on the other digestible proteins. The trypsin inhibitor protein-trypsin enzyme interaction causes the pancreas to produce excessive amounts of trypsin enzymes and thereby causes the pancreas to increase beyond its normal size. Furthermore, the interaction also causes the body's ability to digest proteins to decrease dramatically.
Prior art methods have used heat to deactivate the trypsin inhibitor proteins by denaturing them. Denaturing of proteins occurs when proteins change their structural form. When heat is used, the trypsin inhibitor proteins are denatured so that the bonding sites between the trypsin inhibitor proteins and the trypsin enzymes become inaccessible to the trypsin enzymes. Although the heat eliminates the trypsin inhibition problems, it decreases the digestibility of the other proteins because it denatures the other proteins present in the soy meal. The trypsin enzymes cannot access the sites where the trypsin enzyme cleaves the amino acid bonds in the proteins. Thus, the use of heat results in denatured proteins, causing the NSI of the resulting product to decrease significantly. Therefore, a soy meal treatment process meeting the following objectives is desired.